Reduction of disturbing voltages in electric circuits



Dec. 25, 1934. H. A. RHODES 1,985,353

REDUCTION OF DISTURBING VOLTAGES IN ELECTRIC CIRCUITS Filed Sept. 13,1955 Z00ui INVENTOR ATTORNEY Patented Dec. 25, 1934 UNITED STATESREDUCTION OF DISTURBING VOLTAGES IN ELECTRIC CIRCUITS Harold AnsonRhodes, Montclair, N. 5., assignor to American Telephone and TelegraphCcrnpany, a corporation of New York Application September 13,1933,Serial No. 689,325

5 Claims.

This invention relates to reduction of disturb ing voltages and currentsin transmission lines and, more particularly, to means for reducingnoise frequency voltages and currents in signaling and other circuits bymeans of amplifiers with feed-back connections.

The invention is related to such a circuit as shown in Patent No.1,773,772 to Berthold of December 30, 1926, in which a shunt series or aseries shunt connection of a vacuum tube to a line is made in a mannertherein fully described. I find certain advantages in what may be calleda shunt-shunt connection, one of which is freedom from concern as tophase and amplitude adjustment inasmuch as the circuit which I willdisclose automatically takes care of these.

The invention will be better understood by ref erence to the followingspecification taken in con nection with the accompanying drawing, inwhich Figure 1 shows a circuit arrangement for reducing or eliminatingdisturbing effects which may arise in a source of E. M. F.; Fig. 1ashows an equivalent circuit to Fig. 1; Fig. 2 shows an application ofthis circuit arrangement with slight modifications to eliminatedisturbances which may originate in a generator used for such a load asa storage battery; and Fig. 3 shows an arrangement in connection withdisturbances which may originate in a circuit loop such as atransmission line or a portion thereof.

Referring more particularly to Fig. 1, there is shown a generator E1associated with line L1 going to any suitable load. Such a generator asE1, which may be a D. C. or an A. 0. generator, will ordinarily havepresent in it certain undesired frequencies such as harmonics which maybe of serious disturbance in connection with the load, and the purposeof this invention is to very substantially reduce the effects of suchdisturbances. I accomplish this by the network which is shown asconnected in parallel to the line L1. This network is shown asconsisting of a filter F1 connected directly in shunt to the line oracross the terminals of the generator and feeding into the input of anamplifier A1. If desired, this may then feed into a second andadditional amplifiers A2, although these additional amplifiers may notbe necessary. The output of the last amplifier is connected directly inshunt to the line or across the terminals of the generator, thusproviding, if one wishes to look upon it in that way, a feedbackarrangement from the input to the output of the amplifier. Also, in theoutput circuit I would, in general, desire to introduce some filteringcircuit such as that indicated at F2.

In operation, the filters F1 and F2, used separately or together, are ofsuch a character as to offer a high impedance to the fundamentalfrequency of the generator E1, or such other frequencies from thegenerator as it may be desired (Cl. I'll-97) to transmit along the lineL1. On the other hand, the filter readily transmit those frequencieswhich it desired to suppress. These will then operate on the tube orseries of tubes, in such a manner that the output circuit of the lasttube A: represents a low impedance shunt across the generator terminalsfor those frequencies which passed through the filters F1 and F2. It isapparent that the effectiveness of this shunt depends upon the generatorand load inipedances as well as upon the overall amplification of theseries of tubes. At the same time it is ineffective as a shunt so far asthe fundamental or other frequencies which it is desired to transmitdown the line L1. The circuit as a mole then may be looked upon as avariable shunt across the generator, selective for those frequencieswhich pass the filter F1.

The operation of the circuit may be more clearly set forth through asimple analytical expression which is now derived. The circuit of Fig. Imay be represented conventionally in Fig. 1c, in which the effectivevoltage set up in the output of the amplifier is given by Where mrepresents the ratio of the open circuit voltage at the circuitterminals of the output filter to the voltage impressed at the circuitside of the input filter. An application of Kirchoifs laws will readilyyield. the value of the current I1 as from which it then develops that IT 1 m To avoid singing itis assumed that the amplifier is so designedand connected that the part of the output voltage fed back to the inputhas no component in phase with the input. It is apparent that theeffectiveness of the device may be controlled, to an important extent,by the relative values of the impedances. Thus, if Zo=Zb=Zg then And, ifthe effective value of m for the tube or series of tubes takes on suchmoderate values as 30, it will be noticed that the disturbances will bereduced by a factor of approximately 16. It is understood, of course,that these values are given for illustrative purposes only.

Fig. 2 shows a modification of the circuit of Fig. 1, the applicationbeing particularly to that of a generator used for charging a storagebattery, which storage battery in turn may be used for supplying powerto some other circuit such as telephone circuits. Such generators as E2,here shown as a D. C. generator, are ordinarily subject to certainfluctuations, such as harmonics due to slots and commutation, which maybe par ticularly serious in the neighborhood of 800 or 1200 cycles. Thecircuit arrangement is essentially the same as that of Fig. 1, exceptthat the filter in this case takes on the form of condensers which serveto block out the D. C. voltage from the amplifier and pass allfrequencies above zero. Inasmuch as a storage battery has ordinarily avery low internal resistance, and inasmuch as the bus bars leadingthereto are also of relatively low resistance, it is desirable that theshuntimpedance shall be of very low value for the disturbing frequenciesto be excluded. For this reason it would ordinarily be desirable to usea step-up transformer in the input of the amplifier, and a stepdowntransformer in the output of the amplifier in a manner, and for areason, which will be readily understood by those skilled in the art. Inthis circuit only one amplifier is shown, but it is understood that aseries of amplifiers may be used, as shown in Fig. 1.

Fig. 3 shows a modification of the circuit adapted for reducingdisturbances such as may be picked up inductively by a signaling line Tadjacent to section L" of a power line. In this case theamplifier-filter combination of Fig. 1 is connected directly across theline and protects the section L" from disturbances which may arise inthe generator or in the section L. The filters are designed to readilypass those frequencies which are disturbing, but to exclude those whichare properly to be transmitted over the line from any A. C. source, hererepresented by the generator E3.

Various modifications and applications of this circuit will now beevident to those skilled in the art without departing from the spirit ofthe invention as defined in the claims.

What is claimed is:

1. In an electrical system comprising a generator, a transmission lineand a load, means for eliminating disturbing frequencies arising in thegenerator or the line, said means consisting of an amplifier with itsinput circuit and its output circuit bridged across the line, and meansto pass to the amplifier only those frequencies undesired in the load.

2. In a system for eliminating harmonics and other disturbing effects ina transmission line, an amplifier with its input circuit and its outputcircuit connected directly together and in turn bridged across the lineand having such gain characteristics as to oifer a low shunt impedanceto undesired frequencies.

3. In an electrical system, means for eliminating disturbing frequenciestherefrom, said means consisting of an amplifier with its input circuitand its output circuit bridged across the system in such phaserelationship as to offer a low shunt impedance to undesired frequencies,a filter in the input circuit and a filter in the output circuit of theamplifier, which filters pass the undesired frequencies and exclude thedesired frequencies from the amplifier.

4. A systni for eliminating harmonics and other disturbances from atransmission line consisting of an amplifier with its input circuit andits output circuit bridged across the line, the output terminals of thefilter being so poled with respect to the input terminals that theamplifier output offers a shunt across the line of low impedance for thefrequencies to be suppressed, and means associated with the amplifier topass only the undesired frequencies to the amplifier.

5. In an electrical system comprising a D. C. generator giving rise todisturbances, a storage battery to be charged thereby and signalingcircuits adjacent thereto, connections from the generator to the storagebattery, means for eliminating from the adjacent circuits disturbancesinherent in the charging generator, said means consisting of anamplifier with its input circuit and its output circuit bridged acrossthe generator, and condensers in the input circuit and in. the outputcircuit to block D. C. current from the generator to the amplifier.

HAROLD A. RHODES.

